This document discusses time series analysis. It defines a time series as values of a variable ordered over time. Examples of time series include climate data, financial data, and demographic data. Time series analysis is important for understanding past behavior, predicting the future, evaluating programs, and facilitating comparisons. Components of a time series include trends, cyclic variations, seasonal variations, and irregular variations. Several methods are discussed for measuring and decomposing these components, including moving averages, least squares, and seasonal indices.